Due to size and weight reduction of electronic devices and their improved performance, the amount of heat that generates in a semiconductor device tends to increase. In recent years in a motor controlling field, a power semiconductor having a large band gap such as silicon carbide or gallium nitride has been developed for applications in which high voltage or high current is required such as an electric power device, a vehicle, or a machine tool. Such a power semiconductor can operate at a higher temperature compared with a conventional silicon semiconductor because the semiconductor element itself has high heat resistance.
In order to take advantage of such characteristics of the power semiconductor, a bonding material having an excellent thermal conductivity is required. In recent years, a paste containing nano-sized metal fine particles has been studied as a bonding material having a high thermal conductivity. In a bonding method using such a paste, a sintering phenomenon of metal particles is utilized for the bonding.
A wide variety of studies have been developed for such a bonding method that utilizes sintering of metals. For example, Patent Literature 2 discloses a sintering preform including a carrier having a surface that has at least one structuring element containing hardened paste, wherein the hardened paste contains (a) metal particles having a coating that contains at least one organic compound; and (b) at least one sintering aid. Patent Literature 2 explains that the sintering aid is capable of ensuring a burning off of the coating compounds during the sintering process, and discloses (b1) organic peroxides, (b2) inorganic peroxides, (b3) inorganic acids, (b4) salts of organic acids, (b5) ester of organic acids, and (b6) carbonyl complexes as the sintering aid.
Patent Literature 1: Japanese Patent Laid-Open No. 2006-352080 Patent Literature 2: Japanese Patent Laid-Open No. 2012-60114
However, the sintering aids disclosed in the above Patent Literature 2 are still insufficient in view of their effect on sinterability of bonding materials, and further improvement has been desired.
Accordingly, an object of the present invention is to provide a bonding material excellent in sinterability, thereby a bonding layer having an improved thermal conductivity is provided.